Problem with changing username on XP

Hi,

I have a problem with changing the 'real' username of an account on an XP PC. With 'real' username, I mean the one you find by right-clicking the 'My Computer' icon, then 'Manage', then 'Local users and groups' and finally 'Users'. Here you find a list with all the users on the PC and one of them is my account. The guy who configuered my PC simply called it 'User' and I'd like to change it to my name. Using the 'User Account' tab in control panel only changes the 'Full name' but not the 'Name' of the account.

So if anyone has a clue, please reply

thx